The present invention relates to diaphragm springs, especially for use in friction clutches. More particularly, the invention relates to improvements in diaphragm springs of the type wherein a circumferentially complete outer marginal portion surrounds an annulus of substantially radially inwardly extending prongs which alternate with slots and whose tips surround a substantially centrally located opening.
A diaphragm spring of the above outlined type can be installed between two annular seats which are carried by the cover of a friction clutch, and the tips of the prongs are preferably located at the same level, as considered in the axial direction of the friction clutch, to thus ensure that all of the tips can be engaged by a release bearing when the condition of the clutch is to be changed by pivoting the spring between its seats.
The trend in the automobile industry continues in a direction toward the production of smaller and lighter vehicles without affecting their performance. In fact, the performance of progressively smaller and lighter vehicles is on the increase. Each and every component of the vehicle must or should contribute to the goal of reducing the size and weight, with simultaneous improvement of performance, and this evidently includes the clutch or clutches which are used in the vehicles. Thus, friction clutches which are used in modern automotive vehicles must be compact and of lightweight construction, and their specific performance must be even higher than that of heretofore used bulkier and heavier clutches. On the other hand, the manufacturer of clutches has limited freedom as concerns the selection of materials for some or all of the clutch components, not only because of the cost factor but also as regards the ability of selected materials to stand the stresses which develop in the friction clutch of an automotive vehicle. An important parameter which requires serious consideration is the ability of selected materials to withstand thermal stresses which develop when the clutch is in use. For example, the useful life of friction linings decreases proportionally with increasing temperature. Moreover, distortion of components of a friction clutch also becomes a serious problem at elevated temperatures. In friction clutches wherein the friction linings are mounted on and secured to elastic segments, pronounced rise in temperature is likely to entail setting or even distortion of such segments with attendant adverse effects upon the mode of engagement or disengagement of the clutch and the comfort to the driver and other occupant(s) of the vehicle.
Commonly owned German Pat. No. 1,294,228 proposes to remove friction heat which develops on actuation of a friction clutch. In accordance with the teaching of this patent, the clutch plate is provided with aerating blades which induce the flow of a stream of cool air when the clutch plate rotates. It has been found that such proposal is unsatisfactory when the friction clutch employs a diaphragm spring of the aforementioned type, namely, a spring wherein the radially or substantially radially inwardly extending prongs alternate with rather narrow slots. The combined area of such slots does not suffice to allow for the flow of requisite quantities of cooling air through the clutch, i.e., the blades of the clutch plate are incapable of drawing requisite quantities of air through the slots of the diaphragm spring so that the capacity of such blades to furnish a satisfactory cooling action cannot be utilized in full. In other words, the prongs of the diaphragm spring act not unlike flow restrictors by throttling the flow of air through the slots when the clutch plate rotates and its blades tend to draw air through the diaphragm spring. The centrally located opening of the diaphragm spring is of no help because it is overlapped by the customary release bearing which prevents the flow of substantial quantities of air through the opening.
German Utility Model No. 6 606 711 proposes to provide the slots between the prongs of the diaphragm spring with enlarged portions which are obtained by reducing the width of the neighboring portions of the prongs. Such proposal is unsatisfactory because the enlarged portions of the slots weaken the prongs, i.e., the required strength of the prongs imposes limits upon the dimensions of the enlarged portions of the slots. The end effect is that the rate of air flow through such slots still fails to ensure adequate cooling of all temperature-sensitive components of the friction clutch.